An example of the use of a hot-swap power controller is in a server, where expansion cards may be added by inserting the cards into empty slots in the server. The cards have terminals that mate with terminals in the slot. The mated terminals pass information to and from the card as well as supply power to the card. Typical voltages supplied to the slot power terminals are 12 volts and 3.3 volts.
One or more power controller ICs selectively couple the 12 volt and 3.3 volt power supply voltages to the corresponding slot terminals based on whether certain conditions are met. For example, the power supply voltages should only be applied to the slot terminals if: 1) there is a card inserted into the slot; 2) the supply voltages are at their proper levels; and 3) there is no fault condition, such as an over-current. Typically, if these conditions are met, which may be determined in a matter of milliseconds, the power controller couples, or continues to couple, the power supply voltages to the slot.
Once the above conditions are met, power controllers typically generate a single “power-good” signal for application to an external system processor that is used to convey that the power system is working properly. The power-good signal indicates to the external system processor that it is now okay to communicate with the card since the card is receiving the proper power.
However, some cards require some finite time after the power-good signal is asserted before the card is stable and fully operational. For example, a voltage regulator in the card may need on the order of 100 ms to reach a steady state operating condition. Similarly, capacitors and other energy storing devices in the card may need time to fully charge before the card is fully operational. Further, there may be routines that the card must first carry out before being ready to communicate with the external system. Therefore, there is a period between when the power-good signal is asserted and when the card is ready to properly operate. Using the card within this period may cause errors in the card's processing.
Further, if the card is up and running and it is detected that any one of the above conditions not being met, the typical power controller then instantly removes power from the card and simultaneously deasserts the power-good signal, preventing the system from further communicating with the card. Such abrupt termination of control to the cards may not allow the card to properly shut down.
The above problems are also applicable in many other situations not relating to cards in a slot.
It is desirable to improve the performance of an electronic system where a power-good signal generated by a power controller is used to signal to an external processor that satisfactory power is applied to certain equipment.